<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta http-equiv="X-UA-Compatible" content="IE=edge" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
  </head>
  <body>
    <div class="parent">
      <div class="test"></div>
    </div>
  </body>
</html>
<style>
  .parent {
    border: 2px solid #333;
    width: 100px;
    height: 100px;
    position: relative;
  }
  .test {
    width: 40px;
    height: 40px;
    background-color: pink;
    position: absolute;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
    margin: auto;
    
  }
</style>
